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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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32                                 ALASKAN GLACIER STUDIES
It is partly the presence of the ablation moraine on these piedmont glacier bulbs that permits them to remain in a temperate climate so far from the mountain front and essentially at sea level. Without the protection from the morainic cover these bulbs would of necessity waste away; with it they linger for scores of years even when all further ice supply ceases. How slowly the ice wastes is attested by the fact that dense forests thrive in the morainic soil that covers the glacier.
When the ice melts entirely away the ablation moraine forms a thin, irregular veneer on the surface where the glacier bulb formerly stood, and the sites of lateral moraines are marked by benches and terraces of morainic drift; but terminal moraines are not extensively developed at the front of the piedmont ice bulbs, though they are developed at the fronts of glaciers which terminate within their mountain valleys, and probably also in front of those which end as tidal glaciers. The failure to develop terminal moraines around the front of the piedmont bulbs is easily understood when one considers that the ice in them is either stagnant or so slowly moving that very little debris is brought to the glacier end, and that, therefore, there is no opportunity for* notable concentration of deposit.
Instead of moraines around the periphery of these piedmont bulbs, the frontal accumulations that are most noteworthy are those brought and deposited by streams. There is much melting over the entire bulb area and even in the mountain valley above it, and this abundant water is supplied with great quantities of sediment. Streams issue from various portions of the ice front, some of them very large, and all heavily charged with sediment, varying in texture from fine clay to large pebbles and small bowlders. Much of this sediment must be quickly deposited on the plains that intervene between the ice front and the sea and that are themselves the product of this same stream deposit. If the ice of the piedmont glaciers of the Yakutat Bay region should melt away, without further change, the position of their fronts would be traced by a series of alluvial fans sloping away from the ice, while on the site of the ice itself there would be a thin, hum-mocky deposit of bowlder strewn moraine derived from the ablation moraine of the glaciers. Stream deposition is exceedingly active in this region of abundant water supply and sediment load; but moraine deposit is slow and quite ineffective.
The Glaciers of Yakutat Bay. As has been stated, there are scores of glaciers in and near Yakutat Bay, but the great majority have as yet received no detailed study, because they are small individuals in a region of much larger glaciers, and because they present no features of exceptional interest, in a region where a number of the glaciers have features of decided interest. Some of these smaller glaciers were studied and photographed during the expeditions of 1906 and 1906 and are briefly described in the reports upon the work of those years, but in the National Geographic Society's expeditions of 1909-10 attention was paid to only the larger glaciers, and those smaller ones that were of special interest. In later chapters the results of these studies, in the light of our previous knowledge of them, are stated in detail; here it is intended merely to briefly characterize and locate these more important glaciers.
Beginning with the western portion of the area, there is the Malaspina Glacier, the largest of all, a vast piedmont ice plateau made by the union of the piedmont bulbs of several large glaciers and many smaller ones. Most of its periphery is covered by ablation moraine, and in places this moraine supports a forest of alder, cottonwood, and spruce. The easternmost tributary to the Malaspina is Hayden Glacier, which, however, contri-